50% water change and still 20ppm nitrates

[naesco]

Milan I understand your tank is running for less than 5 month.
With respect, you need to have patience.

You need a skimmer,lighting, live rock and sand and di/ro water to replenish due to evaporation and a good test kit.

Stop using all of the additives any of the other equipment you are or are planning to use.

Feed substantially less than you are presently.

Do a weekly water change of 10% ensuring that the water has been throughly mixed 24 hours before adding it to your tank.

Keep your hands out of the water but remove the slick with a plate as discribed before daily.

Do not add any more animals to your tank.

Take a breather relax you will have a problem free tank if you take the patience to allow your tank to get there.

With confident test kit post all the parameters of your tank and let us go from there